The present invention relates to objects (for example, golf balls) which have an outer surface that contains solvent-activated and solvent-sensitive color-forming compositions, methods of making such objects and methods of using such objects.
Prolonged exposure to, or immersion in, certain solvents (e.g., water) can adversely affect the physical, chemical and mechanical properties of some polymer materials, composite materials, and synthetic construction materials. For example, the exterior of golf balls typically consists of one or more polymer materials. A golf ball that has been submerged in a water hazard for an extended period of time will exhibit inferior flight characteristics compared to a new golf ball, despite the superficial similarity in appearance of the two golf balls (Golf Digest, September 1996). In some instances, the diminished performance of certain materials caused by prolonged exposure to a solvent is temporary and mostly reversible if the solvent is removed by drying the affected materials. In other situations, the effects are permanent and performance is irreversibly damaged. In certain situations, any exposure to a solvent, however brief, may create performance concerns. Thus, there is a need for a color-based indicator that can be incorporated into various solvent-sensitive materials which will alert the user to the possibility that the performance of the materials has been compromised by exposure to, or immersion in, a given solvent. Ideally, color formation would be either reversible or permanent based on different formulations of the indicator and the material it is combined with.
Several water-sensitive color systems currently exist. U.S. Pat. No. 5,130,290, Tanimoto, issued Jul. 14, 1992, discloses a water-sensitive coloring sheet which includes a substrate and a water-sensitive coloring layer containing an unencapsulated color developing material that reacts with a dye when the coloring layer is wetted. The inclusion of a desensitizing material in this system results in a reversible color formation system (i.e., the removal of water results in the removal of the color). U.S. Pat. No. 5,501,945, Kanakkanatt, issued Mar. 26, 1996, discloses the concept of a reversible system in which water sensitive chemichromic dyes are incorporated into polymers used for various packaging applications. U.S. Pat. Nos. 5,823,891 and 5,938,544, both to Winskowicz, issued Oct. 20, 1998 and Aug. 17, 1999, respectively, disclose a color-forming system for use with golf balls which utilizes a water permeable covering over the core of a golf ball, and a water soluble pelletized or microencapsulated colored dye near or within the covering.
All of the discussed systems require some type of colored dye which when subjected to the correct stimulus undergoes a color change. Such dyes must often be processed, i.e., pelletized or microencapsulted, before they can be incorporated into a particular material. Processing dyes in this manner adds difficulty and expense to the process of creating a water-activated color-forming material. Furthermore, these dyes may be removed by simply bleaching the colored material.
The present invention provides an object which, in its outer surface, contains a color-forming composition which comprises a solvent-absorbing material that is generally a polymer; a color-former compounded with the solvent-absorbing material, where the color-former functions as a metal chelating agent; and metal ions capable of forming a chelate complex with the color-former as the solvent-absorbing material absorbs a solvent, resulting in a detectable color change of the composition. These components are present in an effective amount such that when the outer surface of the object is exposed to a solvent for at least two days, a distinct color change is observable and this color change is generally irreversible. The present invention also provides a method for indicating exposure of the color-forming composition to a solvent, wherein the color-forming composition is to be used on the outside surface of objects.
Solvent-absorbing polymers suitable for use in the present invention include, for example: polyethylene acrylic acid, polyethylene methacrylic acid, and copolymers thereof; terpolymers of polyethylene, an acrylic acid and an acrylate; polyurethane; poly-(acrylonitrile-butadiene-styrene); polyvinylchloride; polypropylene copolymer; polystyrene; silicon elastomers; organic rubbers; and combinations thereof.
Preferred metal ions which are suitable for use in the present invention are selected from the group consisting of Na+, Li+, Zn2+, Fe3+, Fe2+, Ca2+, Mg2+, Li+, Ti2+, Ti4+, Mn2+, and combinations thereof.
Two types of color-formers may be used in the present invention: one which produces a permanent color change that is not reversed by removal of the solvent from the solvent absorbing material; and another which provides for a reversible color change when the absorbed solvent is removed from the outer covering of the object.
The color-formers which are used to produce the permanent color change are present in an amount of from about 0.1%, by weight to about 2.5%, by weight. They are generally 1,2-dihydroxybenzene derivatives which include, but are not limited to 1,2-dihydroxybenzene, 3-methylcatechol, 4-methylcatechol, 4,5-dihydroxy-1,3-benzenedisulfonic acid disodium salt and 1,2,3-trihydroxybenzene and mixtures thereof Reversible color-formers are also present in an amount of from about 0.1% to about 2.5%, by weight. They are typically fluoran derivatives substituted with at least one amine group at positions 3 and/or 6. Examples include, but are not limited to, 3-diethylamino-6-methyl-fluoran, 3-dimethylamino-6-methyl-fluoran, 3-dimethylamino-6-methyl-7-anilinofluoran, 2-anilino-3-methyl-6-dibutylaminofluoran, 3-diethylamino-6-methyl-7-anilinofluoran, and 2-anilino-3-methyl-6-diethylaminofluoran and mixtures thereof.
The reversible color-formers may be augmented with a fixative that renders the reversible color change more permanent, depending on the cumulative degree of reaction between the components. The fixatives of the present invention are generally phenolic-based compounds, such as salicylic acid or bisphenol-A, the acetate derivatives thereof and mixtures thereof.
The color-forming compositions of the present invention are white or colorless after initial processing and do not change color until solvent is absorbed. These color-forming compositions are essentially xe2x80x9caquachromic,xe2x80x9d meaning that color change occurs upon exposure to water, but are not xe2x80x9chydrochromic, xe2x80x9d because exposure to moderate humidity alone does not initiate a color change. Once the color change has occurred, the color-forming compositions of this invention are generally unaffected by treatment with typical solutions designed for color removal for extended periods of time. The color-forming compositions of the present invention can have multiple uses, including use as an outer covering for golf balls, whereby prolonged exposure of the color-forming composition to a liquid, such as water, results in a detectable color change of the composition.